One-way clutches having tiltable sprags disposed between concentric rotatable members for controlling torque delivery are known. The concentric rotatable members, typically called inner and outer race members, are selectively coupled and uncoupled by the sprags. The sprags are customarily arranged in an annular configuration having their opposite end portions in frictional engagement with the inner and outer races. The sprags serve to interlock the races or release the races as the sprags are tilted within the annular recess by rotation of the races. In this manner, the one-way clutch is automatically conditioned for driving or overrunning operation responsive to the direction of rotation of the races.
When torque is delivered to the clutch in one direction, the races freewheel and negligible torque is transferred. When the direction of torque delivery is reversed, the sprags tilt into wedging engagement with the races, substantially preventing relative rotation of the races, and accommodating torque transfer.
In order to assure smooth operation of the one-way clutch, the driving loads must be shared equally among the sprags. If a load is transferred through only a few of the sprags, a condition known as "rollover" can occur. In this situation, the driving torque may force one or more of the sprags over center resulting in failure or permanent deformation of either the sprags or the races.
Another condition to be avoided is known as "popout" or "popping" in which the loaded springs suddenly lose static contact with one of the race surfaces, resulting in rapid rotation of sprags to the extreme overrunning position. "Popouts" are caused by sudden release of the load, vibration, or low friction conditions. After "popout" has occurred, one or more of the sprags may fail to engage upon initiation of reverse rotation, due to impact damage.
In order to prevent rollover and reduce damage from popping, some one-way clutches include inner and outer cages in order to keep all of the sprags at substantially the same angular position. These clutches are said to be fully phased.
One-way clutch mechanisms with tiltable sprags have been designed having various race, cage and spring configurations in attempts to provide improved clutch systems. For example, in U.S. Pat. No. 3,324,980 to Rojic et al., the sprags are positioned for engagement by a single elastomer cage with energizing fingers. Since the energizing fingers alone contact the sprags, phasing of the sprags is not achieved. Other patents in which the sprags are free to rotate independently and are not phased are shown, for example, in U.S. Pat. No. 2,753,027 to Troendly et al., U.S. Pat. No. 2,824,635 to Troendly et al., and U.S. Pat. No. 4,880,093 to Message. In the devices shown in these three patents, a single metal cage is used to separate the sprags and a metal ribbon spring is positioned in close proximity to the cage in order to tilt and bias the sprags.
Other single cage one-way clutches are shown in U.S. Pat. No. 4,867,292 to Hartig and U.S. Pat. No. 5,335,761 to Leitz. The Hartig patent discloses a clutch with a single cage with independent energizing springs for each sprag. These independent springs do not provide phasing of the sprags. In Leitz, the clutch has a plastic single cage and a metal ribbon spring placed radially outwardly of the cage. Although phasing of the sprags is secured by Leitz, the metal ribbon spring is relatively fragile affecting the durability of the clutch.
A double plastic cage clutch mechanism is shown in U.S. Pat. No. 4,998,605 to Ferris. This clutch has a plastic inner cage and a plastic outer cage with energizing fingers on one of the cages. Although the two cages act to provide phasing of the sprags, the structure is difficult to manufacture and utilizes a large amount of material. Also, the plastic material is not very durable when used as a spring. Further, the outer wedging surfaces of the sprags are limited in size to fit inside the outer cage windows and thus may have a smaller wedging surface decreasing the torque capacity of the clutch.
Another double-cage clutch design is shown in U.S. Pat. No. 2,824,636 to Troendly et al. This patent discloses a highly successful double-cage sprag clutch in which the sprags are fully phased by the inner and outer cages. The cages are made of metal with specifically defined windows and a ribbon spring is positioned between the two cages for biasing the sprags.